Ankylosing spondylitis is a relatively benign disease, and many patients have a good prognosis with early diagnosis and treatment. Early pathologic changes in sacroiliitis include subchondral granulation tissue formation, histologically visible synovial proliferation and aggregation of lymphocytes and plasma cells, lymphoid follicle formation, and plasma cells containing IgG, IgA, and IgM. Bone erosion and cartilage destruction follow, followed by progressive replacement by degenerating fibrocartilage and eventually bony ankylosis. In layman’s terms, the early pathology is inflammatory changes, and the mid- to late-stage pathology is fibrocartilage formation and bony ankylosis. The inflammatory changes are reversible, whereas once bony ankylosis occurs, it is irreversible. The early stage is the basis for the pathological changes that occur in the middle and late stages, so it is important to actively control the inflammation in the early stages of the onset of compulsory spondylitis for a long time so that the later lesions do not appear. Therefore, I recommend every ankylosing patient to keep the inflammation under control in the early stages of the disease so that the lesions do not appear in the middle and late stages and to avoid aggravation of the disease.